We propose to study the structure and enzymatic properties of the reverse transcriptase from HIV - the virus that causes AIDS. X- ray crystallographic structure determination is a central aim. A long-range objective is to use three-dimensional structural information for drug design, initially by understanding the basis of inhibition by AZTTP. HIV reverse transcriptase (p64) has been cloned and overexpressed in E. coli and purified to homogeniety. Efforts at crystallization are in progress. In order to define potentially crystallizable complexes, we will use nuclease and phosphatase protection to determine how interaction with the enzyme depends on length and sequence to a synthetic template-primer and to determine the length of the synthetic template-primer "covered" by p64. We will use the "optimum" synthetic template-primer thus defined for studies of kinetic properties of the polymerase, including inhibition by AZTTP and related drugs. End-deletion mutagenesis and limited proteolysis will be used to characterize stable domains. In particular, we will study the two aminoterminal fragments, properties of p50 and p35, stable, overproduced species with naturally-occurring counterparts. Site-directed mutagenesis and chemical modification will be used to define active-site residues.